See also at:http://io9.com/?_escaped_fragment_=5060911/magnetic-anomaly-map-of-the-world

"This map shows areas on the globe where there are disturbances in the Earth's magnetic field. Here, red indicates a stronger magnetic tug, and blue a weaker one (white lines are the edges of tectonic plates). As you can see, disturbances are fairly regularly distributed, but that doesn't stop UFO enthusiasts from saying aliens have a hand in these magnetic fluctuations. Science, however, has a slightly different explanation for why certain objects (including submarines) create a shift in the magnetic field."